Production method for chip-form film-forming component

ABSTRACT

A description is given of a high frequency filter comprising microstrips. The filter comprises at least two resonators ( 16, 18 ) which each have, as frequency-determining elements, a first straight microstrip section ( 28 ) and a second straight microstrip section ( 30 ), which are parallel next to each other, and also a capacitor assembly ( 22 ). In each resonator the capacitor assembly is connected between first ends of the microstrip sections and each resonator is exclusively connected to ground at the second ends of the microstrip sections. In each resonator ( 16, 18 ) the sum of the two microstrip sections acts as inductive lement. The resonators ( 16, 18 ) therefore act in the same manner as a resonator having a single microstrip, the length of which corresponds essentially to the sum of the lengths of the first microstrip section ( 28 ) and the second microstrip section ( 30 ). This construction of a filter allows a shorter design compared to conventional filter structures.

The invention relates to a high frequency microstrip filter.

In the high frequency range, the use of microstrips in the constructionof filters is known. Microstrips are strip-like flat conductors whichare attached to an insulating substrate. By suitably selecting thecorresponding parameters (dimensions, dielectric constant of thesubstrate material, etc.) it is possible for microstrips to have adesired impedance response at the frequencies in question. To constructfilter structures, it is known to build resonators consisting ofmicrostrips and capacitors. Microstrips which run parallel to and at adistance from one another are electromagnetically coupled. By suitablyselecting the values and dimensions of the components and also theirarrangement in relation to one another, a desired filter characteristiccan be set.

Such filters are used, for example, in HF transmitters or receivers. Inthis case, bandpass filters, for example, are necessary in order topermit frequency selection. This may be achieved by filters having anadjustable mean frequency. Adjustable filters may also be constructedwith the aid of variable capacitors, for example in the form ofcapacitance diodes (varactors).

U.S. Pat. No. 6,072,999 discloses a receiver comprising a variablefilter. The filter is constructed with microstrips. Resonators areformed in each case of a microstrip and a capacitor assembly, whereinthe capacitor assembly consists of a series circuit of a fixed capacitorand a capacitance diode. A first resonator is connected to an input anda second resonator is connected to an output The microstrips of thefirst and second resonators run in parallel at a distance from oneanother and are electromagnetically coupled. The filter exhibits abandpass characteristic, wherein the mean frequency is variable within arange of about 1-3 GHz. Besides the basic filter structure comprisingtwo resonators, further examples comprising additional,electromagnetically coupled microstrips between the resonators are alsogiven.

US-A-2000/0093400 likewise discloses variable HF filters comprisingmicrostrips. The filters have a number of resonators, formed in eachcase of a microstrip and a capacitor, wherein the microstrips run inparallel next to one another and at a distance apart and areelectromagnetically coupled. An input and an output are coupled to theresonators by direct connection to outer microstrips or byelectromagnetic coupling.

When designing electrical circuits, it is always an objective to reducecosts. A simple design of the circuit with as few components as possibleis therefore desirable. Another aim is to keep the size of electricaland electronic components as small as possible. Since in the case ofmicrostrips the dimensions are critical for the electrical response,strict limits are in this case placed on filters. The length of themicrostrips cannot be reduced without changing the electrical response.

It is therefore an object of the invention to propose a high frequencyfilter comprising microstrips, which has a small size at least in onedimension.

This object is achieved by a filter as claimed in claim 1. Dependentclaims relate to advantageous embodiments of the invention.

The filter according to the invention has at least two resonators, ofwhich one resonator is coupled to the input and one resonator is coupledto the output In one preferred embodiment, the filter only comprisesthese two resonators. However, it is also possible for the filter tohave further resonators.

At least both resonators, preferably all resonators, comprise, asfrequency-determining elements, in each case two straight microstripsections and a capacitor assembly. When considering thefrequency-determining elements, only those which affect the filtercharacteristic in the desired frequency range of the filter areconsidered. As discussed in more detail below, the resonators may have,for example, variable capacitors which may be connected to a variablevoltage in order to vary the filter. Such a connection and thecomponents used for this do not, however, significantly affect thedynamic response in the operating frequency range of the filter and aretherefore not regarded as frequency-determining elements of theresonators.

The main concept of the invention is to reduce the overall length of aresonator by dividing the microstrip of the resonator into twomicrostrip sections. These microstrip sections run in parallel next toone another. The first and second microstrip sections are preferably thesame length. In this case, an actual resonator is not formed by eachmicrostrip section but rather a first and a second microstrip sectiontogether with the capacitor assembly form a resonator. It isparticularly preferred for the resulting filter to have a filter orderthat corresponds to half the number of microstrip sections. Thisdistinguishes the filter from known filter structures in which eachmicrostrip always forms part of an actual resonator and the result isthus filters of a higher order. The first ends of the microstripsections are connected to one another via the capacitor assembly, whilethe second, opposite ends are connected to ground. In the longitudinaldirection, the resonator thus formed is considerably smaller than theresonators of known filter structures.

In order to produce a desired filter characteristic, the resonators ofthe filter are electromagnetically coupled to one another. For thispurpose, in each case one microstrip section runs parallel next to amicrostrip section of another resonator. The filter characteristic canbe suitably adjusted via the degree of coupling. Preferably, theresonators are coupled exclusively electromagnetically, that is to saythat—up to the common ground connection—the frequency-determiningelements are not directly connected.

The capacitor assembly may comprise one or more components. Thecapacitance of the capacitor assembly may be fixed or variable. In onepreferred embodiment, the capacitor assembly comprises a series circuitof a fixed capacitor and a variable capacitor, for example a capacitancediode. A capacitance diode within the capacitor assembly is preferablyconnected to a variable voltage via a high impedance resistor, whereinthe capacitance can be adjusted via the variable voltage. It ispreferred for the capacitor assembly to have a further capacitor besidesthe capacitance diode, wherein both are connected to in each case onemicrostrip section. It is then possible to adjust the capacitance of thecapacitance diode via a DC bias voltage.

The coupling of the input to a first resonator may be effected by directconnection of the input to a microstrip section of the first resonator.Preferably, a T-shaped structure is then formed from the microstripsection and a coupling microstrip, which intersects the microstripsection. It is not necessary for the point of intersection to lie in thecenter; rather, the position can be suitably selected in order to adaptthe impedance of the coupling. As an alternative to the directconnection of the input to the first resonator, an electromagneticcoupling may also be selected, in which a structure composed of a firstcoupling microstrip and a second coupling microstrip that runs at rightangles thereto is formed. Preferably, the first and second couplingmicrostrips are arranged in an L-shape. The second coupling microstripruns in parallel next to a microstrip section of the first resonator andis electromagnetically coupled to the latter.

The coupling possibilities mentioned above in respect of the input alsoapply in respect of the output. Depending on the application, different(symmetrical—asymmetrical) inputs/outputs may be connected to thefilter. The filter itself is preferably designed to be symmetrical.

In one preferred embodiment, the filter is constructed on an insulatingsubstrate, wherein the microstrip sections run on the front side and aconductive layer that is connected to ground is present on the rearside. In each case, the second ends of the microstrip sections of theresonators preferably have a through-connection to the rear side of thesubstrate.

The invention will be further described with reference to examples ofembodiments shown in the drawings to which, however, the invention isnot restricted.

FIG. 1 shows a partially geometric diagram of a first filter circuit.

FIG. 2 shows a partially geometric diagram of the frequency-determiningelements of the filter circuit of FIG. 1.

FIG. 3 shows a partially geometric diagram of a second filter circuit.

FIG. 4 shows a partially geometric diagram of the frequency-determiningelements of the filter circuit of FIG. 3.

FIG. 5 shows a diagram of the front side of a filter.

FIG. 6 shows a diagram of the filter characteristic at different meanfrequencies.

In general, the invention relates to filters in the high frequencyrange, that is to say to frequencies above 500 MHz.

The filters shown in the examples of embodiment are provided for thefrequency range of 1.8 to 2.3 GHz. In an HF transmitter for digitalvideo data (DVB-RCS), a QPSK-modulated signal is to be generated inwhich the undesirable sideband is to be attenuated by at least 60 dBc.The filter used is to be variable in a range of 500 MHz.

FIG. 1 shows a diagram of a first filter circuit 10 proposed for thispurpose. The diagram is partly geometric, wherein the form and relativearrangement of the microstrips used is shown in principle.

The filter 10 has an input 12 and an output 14. A first resonator 16 isconnected to the input 12. A second resonator 18 is connected to theoutput 14. The resonators 16, 18 are designed to be symmetrical with oneanother and are coupled electromagnetically to one another. The filter10 has a connection 20 for a variable voltage VT. Each of the resonatorshas a capacitor assembly 22 consisting of a capacitance diode 24 and afixed capacitor 26. The capacitance diode 24 and the capacitor 26 areconnected in series. The cathode of the capacitance diode 24 isconnected to the variable voltage VT via a high impedance resistor R anda further terminal resistor RT. The resistance of R is at least 5 kΩ,preferably 10-100 kΩ.

Furthermore, each resonator 16, 18 has a first microstrip section 28 anda second microstrip section 30. The capacitor assembly 22 is connectedbetween the first ends of the microstrip sections 28, 30. The secondends are connected to ground. The first and second microstrip sections28, 30 are arranged next to one another, producing an electromagneticcoupling. However, this coupling is not critical for operation. It iseven preferred to arrange the sections 28, 30 a certain distance apartso that the coupling is as low as possible.

The two elements of the capacitor assembly 22, fixed capacitor 26 andcapacitance diode 24, are in each case connected to one end of amicrostrip section 28, 30. The high impedance resistor R is connected tothe respective opposite connection of the elements 24, 26. The anode ofthe capacitance diode 24 is connected to ground via the first microstripsection 28. This makes it possible to apply, at a suitable variablevoltage VT, an appropriate DC voltage in the non-conducting direction ofthe capacitance diode 24, so that the capacitance can be suitablyadjusted within a range. The fixed capacitor 26 acts as an open circuitwith respect to the applied DC voltage VT. Said fixed capacitor isnecessary to generate the DC voltage via the capacitance diode 24,because the second microstrip section 30 is connected to ground at itssecond end.

The first resonator 16 and the second resonator 18 are of identicalconstruction and are connected in an identical manner to the variablevoltage VT. The response of the two resonators 16, 18 is thereforeidentical up to resulting tolerances.

FIG. 2 shows a diagram of the filter 10 of FIG. 1, in which thefrequency-determining elements are shown. The capacitor assembly 22 isshown as a variable capacitor. In each case the second microstripsections 30 of the resonators 16, 18 run in parallel next to one anotherand at a distance apart, so that the resonators 16, 18 areelectromagnetically coupled. A bandpass filter characteristic istherefore produced overall between the input 12 and the output 14,wherein the mean frequency can be adjusted by means of the variablecapacitors 24.

In this case, the microstrip sections 28, 30 in each case do not act asindependent resonators but rather in each case a first and a secondmicrostrip section 28, 30, together with the capacitor assembly 22, forma resonator. Consequently, the filter characteristic is of the secondorder. The order of the filter therefore corresponds to half the numberof microstrip sections. In each resonator 16, 18, the sum of the twomicrostrip sections acts as inductive element. The resonators 16, 18therefore act in the same manner as a resonator having a singlemicrostrip, the length of which corresponds essentially to the sum ofthe lengths of the first microstrip section 28 and the second microstripsection 30. The size of the filter circuit 10 in the longitudinaldirection L shown in FIG. 2 is therefore considerably smaller than whenusing resonators having in each case just one microstrip which is notdivided into sections.

In the filter 10, the resonators 16, 18 are coupled to the inputs andoutputs 12, 14 by direct connection. In turn, a coupling microstrip 32which runs at right angles to the microstrip sections 28, 30 is in asymmetrical manner connected to the input and output 12, 14. Thecoupling microstrip 32 in each case intersects the first microstripsection 28 of the resonators 16, 18. In the example shown, the couplingtakes place at the center. This results in a T-shaped structureconsisting of the microstrip sections 28 and the coupling microstrip 32.In order to suitably adapt the impedance of input and/or output 12, 14,the point of intersection can also be displaced to one or the other endof the microstrip section 28.

FIG. 3 shows a second filter circuit 40. The filter circuit largelycorresponds in terms of its structure to the filter circuit 10 ofFIG. 1. Identical elements bear the same references. Hereinbelow, onlythe differences with respect to the circuit 10 of FIG. 1 will bediscussed.

By contrast with the circuit 10, in the circuit 40 the inputs andoutputs 12, 14 are electromagnetically coupled. The coupling in thiscase comprises a first coupling microstrip 42 which is connected to theinput and output 12, 14 and runs at right angles to the microstripsections 28, 30. The first coupling microstrip 42 forms an L-shapedstructure with a second coupling microstrip 44 that runs at a slightdistance parallel to the first microstrip section 28 of the resonators16, 18. The end of the second coupling microstrip 44 is connected toground.

The second coupling microstrip is in close electromagnetic coupling withthe first microstrip section 28, so that the signal from the input 12 iscoupled into the first resonator 16 and coupled out of the secondresonator 18 to the output 14.

FIG. 4 in turn shows the frequency-determining elements of the filtercircuit 40.

FIG. 5 shows a filter 50 constructed in accordance with the circuit 40.The dark regions are copper structures on an insulating substrate. Onthe rear side of the insulating substrate there is a conductive layerthat is connected to ground. The filter 50 has an input 12 and an output14 and also a connection for the variable voltage VT. The high impedanceresistors R, like the fixed capacitors 26 and the capacitance diodes 28,are discrete components which are soldered onto the surface of thesubstrate. The use of discrete components is advantageous at thecapacitances of a few pF that are preferably used. As an alternative,the components, in particular capacitors having a low capacitance, mayalso be applied to the substrate as printed components. The couplingmicrostrips 42, 44 and the first and second microstrip sections 30, 28of the resonators 16, 18 are formed by the arrangement as shown in FIG.3. The connection to ground is formed by means of through-connections 52to the rear side of the substrate.

The filter 50 has a width of 12 mm and a length of only 10 mm. However,the effective length of the microstrips of each substrate corresponds tothe sum of the individual microstrip sections 28, 30 and is thereforemore than the 10 mm length of the filter 50 in this direction.

FIG. 6 shows the filter characteristic of the filter 6 at different meanfrequencies. The attenuation in dBc is shown against the frequency inMHz. The characteristic for three different values of the variablevoltage VT, that is to say three different capacitances, is shown.

In the abovementioned examples of embodiment of filter circuits, in eachcase two resonators are provided, producing a filter response of thesecond order. It is possible for further resonators to be providedbetween the first and second resonators, the microstrip sections ofwhich further resonators run parallel to the microstrip sections 28, 30of the first and second resonators 16, 18 and are electromagneticallycoupled to the latter.

Further possible modifications to the filter relate to the coupling ofinput 12 and output 14. In this case, various types of coupling known tothe person skilled in the art may be selected. In particular, asymmetriccoupling may be selected.

1. A filter circuit comprising an input (12) and an output (14) and atleast two resonators (16, 18), of which one resonator (16) is coupled tothe input (12) and one resonator (18) is coupled to the output (14),wherein each resonator (16, 18) has, as frequency-determining elements,a first straight microstrip section (28), a second straight microstripsection (30) and a capacitor assembly (22), wherein in each resonator(16, 18) the capacitor assembly (22) is connected between in each casefirst ends of the microstrip sections (28, 30), and each resonator isexclusively connected to ground at the second ends of the microstripsections (28, 30), and wherein the first and second microstrip sections(28, 30) are arranged in parallel next to one another, and wherein ineach case one of the microstrip sections (30) of the resonators (16, 18)is electromagnetically coupled to at least one of the microstripsections (30) of a further resonator (16, 18) by the microstrip sections(30) of the resonators being arranged in parallel next to one anotherand at a distance apart.
 2. A filter as claimed in claim 1, in which thecapacitor assembly (22) comprises at least one variable capacitor (24).3. A filter as claimed in claim 2, in which the capacitor assembly (22)comprises a series circuit of a fixed capacitor (26) and a variablecapacitor (24).
 4. A filter as claimed in claim 2, in which thecapacitor assembly (22) comprises a capacitance diode (24) which isconnected to a variable voltage (VT) via a high impedance resistor R. 5.A filter as claimed in claim 1, in which the first and second microstripsections (28, 30) each have the same length.
 6. A filter as claimed inclaim 1, in which in each case one of the microstrip sections (28, 30)of the resonators (16, 18) is coupled exclusively electromagnetically toin each case one of the microstrip sections of a further resonator (16,18).
 7. A filter as claimed in claim 1, in which between the input (12)and the output (14) there is a filter response of an order thatcorresponds to half the number of microstrip sections (28, 30) of theresonators (16, 18).
 8. A filter as claimed in claim 1, in which themicrostrip sections (28, 30) are attached to a front side of aninsulating substrate, in which a conductive layer on the rear side isconnected to ground, wherein the first and second microstrip sections(28, 30) each have at their second end a through-connection (52) to therear side of the substrate.
 9. A filter as claimed in claim 1, in whichthe input (12) is coupled to a first resonator (16), wherein the inputis connected to a coupling microstrip (32) which runs at right angles tothe microstrip sections (28, 30) of the resonators (16, 18), and whereinthe coupling microstrip (32) intersects the first microstrip section(28) of the first resonator (16).
 10. A filter as claimed in claim 1, inwhich the input (12) is coupled to a first resonator (16), wherein theinput (12) is connected to a first coupling microstrip (42) which runsat right angles to the microstrip sections (28, 30) of the firstresonator (16), and wherein the first coupling microstrip (42) isconnected to a second coupling microstrip (44) which runs in parallelnext to the first microstrip section (28) of the first resonator (16)and is electromagnetically coupled to the latter.